Why might Gen. John Allen, the top U.S. commander in Afghanistan, be facing a court martial?

Thousands of flirtatious emails between Allen and Florida socialite Jill Kelley were discovered during the investigation that revealed the affair between Paula Broadwell and Gen. David Petraeus — the now former director of the CIA. Unlike Petraeus, who retired from the military before he began his affair, Allen is still on active duty, and adultery is a crime under the Uniform Code of Military Justice.